The present invention relates generally to a distillation apparatus for removing impurities or solids from liquids, for example for desalinating salt water or for removing solids from sewage.
In U.S. Pat. No. 3,338,798 of Parr an alternating still desalination apparatus is described which comprises two inverted containers with their lower, open ends submerged in sea water. Each container contains a heat exchanger disposed in the sea water, and the upper end of one container is connected to the heat exchanger in the other container, and vice versa. A reciprocating drive mechanism is provided for simultaneously lowering one container while raising the other container, so that the vapor pressure in the space above the water level in the lowered container is raised, super heating the vapor in that space and forcing it out into the heat exchanger in the other container, while the pressure will drop in the upwardly moving container, causing the water in that container to vaporize. Vapor forced out of one container into the heat exchanger coil of the other container is condensed and distilled water is delivered at the heat exchanger outlet. The disadvantage of this apparatus is that it must be partially submerged in a body of water, such as sea water, and thus must be situated at an appropriate site where it can be submerged. Also, valuable minerals in the sea water cannot be recovered. An alternative embodiment is described, in which two closed and stationary containers are provided which are connected via a piston and cylinder arrangement for alternately increasing and decreasing the pressures in the two containers.